The heart of a computer's long-term memory is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air-bearing surface (ABS). The suspension arm biases the slider toward the surface of the disk and when the disk rotates, air adjacent to the surface of the disk moves along with the disk. The slider flies on this moving air at a very low elevation, fly height, over the surface of the disk. This fly height is on the order of nanometers. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic transitions to and reading magnetic transitions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
In a typical design, the write head includes a coil layer embedded in first, second and third insulation layers, an insulation stack, the insulation stack being sandwiched between first and second pole-piece layers. A gap is formed between the first and second pole-piece layers by a gap layer at an air-bearing surface (ABS) of the write head and the pole-piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic flux in the pole pieces which causes a magnetic field to fringe out at a write gap at the ABS for the purpose of writing the aforementioned magnetic transitions in tracks on the moving media, such as in circular tracks on the aforementioned rotating disk.
In recent read head designs, a spin-valve (SV) sensor, also referred to as a giant magnetoresistive (GMR) sensor, has been employed for sensing magnetic fields from the rotating magnetic disk. This sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer and a free layer, both of which can be made up by a plurality of layers. First and second leads are connected to the spin-valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned substantially perpendicular to the air-bearing surface (ABS) and is relatively insensitive to applied magnetic fields. The magnetic moment of the free layer is biased substantially parallel to the ABS, but is free to rotate in response to external magnetic fields. In the following, substantially parallel means closer to parallel than perpendicular; and, substantially perpendicular means closer to perpendicular than parallel. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
For a current-in-plane, spin-valve (CIP-SV) sensor, the thickness of the spacer layer is chosen to be less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with each of the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal; and, when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin-valve sensor in proportion to cos θ, where θ is the angle between the magnetizations of the pinned and free layers. Since θ is near 90 degrees at zero field, the resistance of the spin-valve sensor, for small rotations of the free layer from 90 degrees, changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin-valve sensor, resistance changes cause potential changes that are detected and processed as read-back signals.
When a spin-valve sensor employs a single magnetic layer as a pinned-layer structure, it is referred to as a simple spin valve. When a spin valve employs an antiparallel (AP) pinned-layer structure, it is referred to as an AP-pinned spin valve. An AP-pinned spin valve includes first and second magnetic layers separated by a thin nonmagnetic coupling layer such as Ru or Ir. The thickness of the coupling layer is chosen so as to antiparallel couple the magnetic moments of the ferromagnetic layers of the pinned-layer structure. A spin valve is also characterized as a top or bottom spin valve depending upon whether the pinning layer is at the top, formed after the free layer, or at the bottom, before the free layer.
Magnetization of the pinned layer is usually fixed by exchange coupling one of the ferromagnetic layers (AP1) with a layer of antiferromagnetic material such as a Pt—Mn alloy with nominally 50 atomic percent Mn. While an antiferromagnetic (AFM) material such as a Pt—Mn alloy does not, in and of itself, have a net magnetic moment, when exchange coupled with a magnetic material, it can strongly pin the magnetization of the ferromagnetic layer.
A current-in-plane, spin-valve (CIP-SV) sensor is located between first and second nonmagnetic electrically insulating read gap layers; and, the first and second read gap layers are located between ferromagnetic first and second shield layers. In a merged magnetic head, a single ferromagnetic layer functions as the second shield layer of the read head and as the first pole-piece layer of the write head. In a piggyback head, the second shield layer and the first pole-piece layer are separate layers.
The ever increasing demand for greater data rate and recording density has lead a push to develop sensors having ever decreasing dimensions, such as decreased magnetic read width (MRW), driven by narrower track widths (TW) of the data recorded onto the magnetic recording disk, and stripe height (SH), which is the distance that the sensor extends back away from the ABS. However, as described above, in order for a magnetoresistive sensor to operate as desired, various layers such as the free and pinned layers must be in essentially single magnetic domain states having magnetizations oriented in desired directions. For example, the free layer must remain biased in a direction substantially parallel with the ABS, while the pinned layer must have a magnetization that remains pinned in a desired direction substantially perpendicular to the ABS. As sensors become smaller, the ability to maintain these magnetic states diminishes greatly. Free layers lose biasing, becoming unstable, and pinned layer magnetizations can flip, a situation that leads to amplitude flipping. Both of these situations render the sensor unusable. A technique for generating a magnetic anisotropy with an easy axis of magnetization in any desired direction in the various layers would greatly facilitate sensor robustness by stabilizing single domain states having magnetizations oriented in desired directions.
In a similar manner, the performance of other components of a magnetic recording system would be greatly improved if a magnetic anisotropy could be generated with an associated easy axis of magnetization that could be oriented in any desired direction. For example, the performance of a magnetic write element, magnetic shields, or a magnetic recording medium could be greatly improved, if a technique existed for orienting the easy axis of magnetization in a desired direction in such devices. Likewise, the performance of magnetic memory cells that incorporate magnetoresistive memory elements can be greatly improved, if a magnetic anisotropy could be generated with an associated easy axis magnetization that could be oriented in any desired direction.